1. Technical Field of the Invention
This invention relates generally to electronic sensor circuits, and, more particularly, to a sensor circuit assembly comprising a sensor integrated circuit and an amplifier circuit distinct from said sensor integrated circuit, wherein all system trim resistors are located on the sensor integrated circuit.
2. Background Information
The present invention has utility in electronic sensor circuits, especially in semiconductor pressure sensor circuits. Pressure responsive transducer circuits are utilized extensively in automobile engine control systems. For example, a manifold pressure sensor and amplifier circuit may provide an analog signal which varies with the engine manifold pressure. An analog-to-digital converter transforms the analog control signal into a digital control signal which is utilized by a microprocessor-controlled fuel injection system.
The operation of most semiconductor pressure transducers and op amps varies with temperature, requiring temperature-compensating techniques and circuitry. U.S. Pat. Nos. 4,326,171 and 4,463,274 disclose temperature-compensating circuits for pressure transducers.
Semiconductor transducer/amplifier circuits may be packaged in several ways. For example, they may be packaged on a printed circuit board. However, the customer is then responsible for performing the necessary trimming operations for temperature compensation and for adjusting the op amp gain. Customers typically may not be qualified or motivated to perform such work. Moreover, resistor temperature coefficients at the board level are not well matched, thus degrading system accuracy.
Another known package is a two-chip system comprising a sensor chip and a second custom chip containing thin-film resistors for temperature compensation and for calibrating and amplifying the output. However, the disadvantages of the two-chip system are that the custom integrated circuit must be redesigned for each advance or alteration in circuit or process technology. Nor can a two-chip system provide necessay flexibility in circuit configuration.
Yet another known package is a hybrid module, comprising a substrate on which is mounted a sensor chip, one or more amplifier chips, and suitable resistors and capacitors which are soldered to metal pads and wire-bonded to interconnecting metal traces. The resulting package may take the form of an encapsulated assembly with leads.
One disadvantage of hybrid modules is that they tend to be very labor intensive because each component has to be individually placed, connected, calibrated, and temperature-compensated.
It is also known to incorporate sensor circuits onto a single integrated circuit device. But even with a fully integrated circuit device it is necessary to adjust or "trim" on-chip passive elements for various purposes, such as setting the transducer offset voltage, the op amp input voltage offset, and resistive values.
An advantage of a fully integrated device is that all trim is performed on a system-wide basis. That is, the op amp gain is set at the same time that the sensor element temperature calibration step is performed. All components on the chip, including the sensor and op amps, are matched with respect to values and temperature coefficients. At trim, all values and temperature coefficients are set.
However, a disadvantage of such integrated circuit devices is that they have relatively long development cycles and are relatively expensive, especially in low-volume applications.
There is therefore a significant need in the semiconductor transducer field to provide customers with a fully system-ready product, which requires no trimming or adjustment by the customer or user. There is also a strong demand by customers for relatively low cost sensor circuits. In addition, customers desire short development cycles for prototype sensor systems, so it would be desirable to provide a sensor assembly that is easy to modify to meet the needs of different customer applications.
Therefore, there is a substantial need to provide a compact sensor assembly that is low in cost, high in quality, and which facilitates a short prototyping cycle and a short manufacturing cycle.